Cathode assembly for electrolytic cell



Sept. 2, 1969 EMERY ET AL 3,464,912

CATHODE ASSEMBLY FOR ELECTROLYTIC CELL Filed May 16, 1966 2 Sheets-Sheet 1 Sept. 2, 1969 A. T. EMERY ET AL 3,464,912

CATHODE ASSEMBLY FOR ELECTROLYTIC CELL Filed May 16, 1966 2 Sheets-Sheet 2 United States Patent 3,464,912 CATHODE ASSEMBLY FOR ELECTROLYTIC CELL Alvin T. Emery, North Tonawanda, and Walter W. Ruthel,

Niagara Falls, N.Y., assignors to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York Filed May 16, 1966, Ser. No. 550,429 Int. Cl. C22d 1/02; B01k 3/04 US. Cl. 204286 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electrolytic cells for the electrolysis of aqueous solutions and more particularly to the cathode assembly of a diaphragm type electrolytic cell particularly suited for the electrolysis of aqueous alkalimetal chloride-containing solutions.

Chlor-alkali diaphragm cells have been used extensively for many years for the production of chlorine, caustic and hydrogen. Over the years, such cells have been perfected to a degree whereby extremely high operating efficiencies are obtained, based on the electrical energy expended. Most recent developments in diaphragm type chlor-alkali cells have been in improvements for increasing the production capacities of individual cells, thereby obtaining a higher production rate for a given cell room area. Chlor-alkali cells have most recently been developed capable of utilizing over 55,000 amperes of current per cell. In order to obtain high efficiencies in chlor-alkali diaphragm cells of such high current capacities, comparable to the more conventional lower amperage cells of about 30,000 amperes, various structural improvements are best incorporated into these high amperage cells to maintain or increase their current and power efficiencies. Mere enlargement of the component parts of such cells, while providing highly eflicient cells, does not always provide the most favorable efficiencies, based on consrtuction costs and operating performance.

It is an object of the present invetnion to provide a cathode structure particularly suited for high amperage chlor-alkali cells whereby a favorable voltage drop is obtained throughout the cathode fingers. It is aouther object of the present invention to provide a cathode construction comprised of reinforced foraminous screen fingers attached to the cathode sidewall in a manner by which improved electrical contact is obtained with greatly reduced copper requirements. These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

In accordance with the invention a cathode assembly is provided for an electrolytic cell comprising a lead-in bus bar, a bus bar strip and a walled enclosure having sidewalls, to which are attached a plurality of internally reinforced foraminous screen fingers, said fingers extending substantially across the interior of said enclosure, said internal reinforcing means being directly attached to at least one side of said enclosure and in electrical contact with said screen fingers, said attachment being adjacent to 3,464,912 Patented Sept. 2, 1969 "ice an externally psoitioned bus bar strip on the exterior of one side of said enclosure, said bus bar strip being of substantially the height of the reinforcing means at the point of attachment thereto and said bus bar strip being directly attached to said lead-in bus bar.

The present invention provides a bus bar assembly for a cathode by which the construction costs of cathodes for electrolytic cells can be greatly reduced and whereby up to about percent of the copper previously required in bus bar connections can be eliminated while substantially mzlilintainmg or improving the voltage drop throughout the ce The invention will be more fully described by reference to the drawing in which:

FIG. 1 is a side elevation of an electrolytic cell constructed in accordance with the present invention;

FIG. 2 is an enlarged partial sectional view of the cell of FIG. 1 along plane 2--2;

FIG. 3 is an enlarged [partial sectional view of the midcatdhode section of the cell of FIG. 1 along plane 3-3; an

FIG. 4 is a partial sectional end elevational view of the cathode fingers and wall enclosure showing part of the cell bottom and illustrating the position of the cathode fingers in relation to the anode blades mounted in said cell bottom.

Because the present invention may be used in many different electrolytic processes of which chlor-alkali electrolysis is of primary importance, the invention will be described more particularly with respect to such processes. However, such descriptions is not to be understood as limiting the usefulness of the present invention.

The electrolytic diaphragm cell 10 of the present invention comprises a cell top 12, a cell bottom 16, and a cathode section having an outer sidewall enclosure 14 and a plurality of foraminous cathode fingers 28. The cell top 12 and the cell bottom 16 are normally constructed of concrete but they can also be of other materials inert to the reaction conditions within the cell. The sidewall enclosure 14 is normally of four sides and of metal to which is attached externally on one side, a plurality of vertically positioned bus bar strips. Electrical contact is made between the bus bar strips 24 and lead-in bus bar 22. A source of electrical current is fed to lead-in bus bar from an adjacent cell, a dynamo, a rectifier, or the The plurality of cathode fingers can be any number from about two to or more but most preferably the number of cathode fingers is about 10 to 30. The number of bus bar strips attached to the exterior sidewall of the cathode can also vary widely from one to the number of cathode fingers and more preferably a number ranging from equal to, to several less, than the number of reinforcing means in said cathode fingers.

Interposed between cell top 12 and outer sidewall enclosure 14 of the cathode is sealing gasket 18. A similar sealing gasket 20 is positioned betweenthe outer sidewall enclosure 14 of the cathode and cell bottom 16. These gaskets serve as both sealing means to prevent the leakage of liquids and gases as well as insulating means to electrically isolate the metal cathode section.

The cathode section is constructed of a conductive metal and preferably a ferrous metal such as mild steel or a ferrous alloy such as stainless steel. However, more conductive metals such as copper, nickel, brass and the like metals can be used since the cathodic potential during cell operation reduces the danger of corrosion of such metals. The internal structure of the cathode is also preferably of a similar ferrous metal such as a mild steel. This internal construction is composed of a plurality of foraminous cathode fingers 28 composed of reinforcing means 26 to which is attached cathode screen 36. In the operation of the cell as a chlor-alkali cell, a liquidpermeable diaphragm is applied or deposited over the screen cathode fingers 28 thereby forming separate anode and cathode compartments. Cathode fingers 28 are in a spaced relationship to each other at a distance such that when the cell is assembled, anode blades 30, which are attached to a conductive material 32, as by embedding in lead or other conductive metal in cell bottom 16, are centered with respect to cathode fingers 28. The conductive metal is subsequently sealed with a nonconductive caustic and/or chlorine resistant sealant 34. The anode blades 30 are thus securely positioned at an equal predetermined distance between the cathode fingers 28.

Reinforcing means 26 is preferably a corrugated ferrous metal plate or sheet which extends across the interior of the cell within cathode fingers 28. Metal reinforcing means 26 is directly attached as by welding to the interior of the bus bar strip 24 side of sidewall enclosure 14. The attachment is preferably made continuous for substantially the entire height of the reinforcing means at the point of attachment. The opposite end of reinforcing means 26 can also be attached to the outer sidewall enclosure 14 on the side opposite the bus bar strip 24 in the same manner. However, such attachment need not provide complete electrical contact with the sidewall. Cathode screen 36 is electrically attached as by welding, riveting, tacking, and the like, to reinforcing means 26.

Bus bar strip 24 and lead-in bus bar 22 are preferably of a highly conductive metal such as copper. Reinforcing means 26 is directly attached to the outer sidewall 14 opposite the externally positioned bus bar strip 24 preferably by welding 25. Such welding between and around bus bar strips 24 provides an increased weld area and excellent electrical conductivity through sidewall 14 to cathode screen 36 by means of reinforcing means 26. To increase conductivity to cathode screen 36, the gauge of reinforcing means 26 can be increased. As such, reinforcing means 26 is preferably of a thickness between about 0.05 to 0.3 inch and more preferably about 0.1 to 0.2 inch.

Conductive copper bus bar strip 24 is preferably substantially the same height as reinforcing means 26 at the point of attachment to outer sidewall enclosure 14. Under such conditions, thecurrent is readily carried to all sections of cathode screen 36 with a minimum travel distance through reinforcing means 26. Bus bar strip 24 is preferably of a thickness less than that of lead-in bus bar 22. The exact dimensions for the bus bars for a particular cell is further dependent on the expected current usage in the cell and the current carrying capacity of the bus bar adjusted accordingly. The width of bus bar strip can also vary depending on a number of factors such as current load conductivity of the metal used, length of the strip, the amount of weld area desired, fabrication costs and the like. A width suitable for most uses is that varying from about the inside width of a cathode finger to about the distance between the internal reinforcing means. The distance between the bus bar strips will of course vary with the width thereof, the distance being up to about the distance between the cathode finger reinforcing means. Thus, in the preferred embodiment a bus bar strip is positioned adjacent to reach reinforcing means and the area between the strips is filled with the welding, the seams of the welding being centered over the place where the internal reinforcing means are joined to the sidewall enclosure. The welding metal is preferably of the same metal as the bus bar strips. This method of attaching the bus bar strips to the cathode sidewall greatly increases the weld area which area forms the lowest resistance contact with the cathode. The height of the strip is as previously described, i.e., substantially canal to the reinforcing means at the point of attachment. This height can further be described as being of more than about one-half of the height of the cathode enclosure.

Immediately above and below the point of attachment of the reinforcing means 26 to the outer sidewall enclosure 14 are gas withdrawal means 38 and caustic withdrawal means 40. Hydrogen gas produced by the electrolysis at the cathode is conveniently taken off through gas withdrawal means 38 into a peripheral chamber surrounding the cathode fingers from which the gas is eventually withdrawn. Also, as brine flows from the anode compartment into the cathode compartment wherein caustic is produced during the electrolysis, caustic withdrawal means 40 is provided for the withdrawal of caustic from the cathode fingers into a peripheral chamber surrounding the cathode fingers from which the caustic is ultimately withdrawn from the cell itself.

Although lead-in bus bar 22 is illustrated as two separate bus bars, a single elongated bus bar can also be used to which one or more current carrying bus bars can be attached. Also, a continuous bus bar strip 24 may be used for attachment directly to the external sidewall enclosure immediately opposite where the reinforcing means 26 is internally attached to the enclosure.

A cathode assembly constructed in accordance with the prior art using a peripheral bus bar surrounding the cathode required 855 pounds of copper to provide a cell voltage of about 4 volts at 55,000 amperes. By the present invention, only 225 pounds of copper are used to obtain the same voltage at the given amperage. By increasing this amount of copper as by using copper in the cathode fingers, the voltage can be reduced over that of the prior art for the same weight copper.

Electrical connection with other cells in a series is made by attaching the anode bus bar of the cell embedded in the concrete cell bottom (not shown) to the cathode lead-in bus bar of the adjoining cell. Connection between the anode and cathode bus bars is made using heavy conductive cables or bars, preferably copper, and bolting or attaching these bars to the lug holes 23 in the lead-in bus bar 22. Generally, the cells are positioned immediately adjacent to each other in a row such that the bus bar connection between cells is of a minimum distance.

In the operation of the cell, as a chlor-alkali cell, an alkali-metal chloride, for example, sodium chloride, is introduced into the cell as a brine stream of desired concentration. The brine level within the cell is brought to a point above the anode blades within the cell. By adjusting the level within the cell, the hydrostatic head or pressure exerted upon the diaphragm covering the screen cathode fingers is varied, thereby varying the flow through the diaphragm. Under normal operation, the height of the brine above the anode blades is about one to 15 or more inches.

As has previously been stated, the cell is useful for the electrolysis of alkali-metal chloride solutions, in general, including not only sodium chloride, but also potassium chloride, lithium chloride, rubidium chloride and cesium chloride. In the electrolysis, using a diaphragm covering the screen cathode, caustic chlorine and hydrogen are produced. Using certain modifications and changes in the method of reacting, such as removing the diaphragm or further reacting the produced caustic and chlorine, alkali-metal chlorates can also be produced by the present cell. Thus, in some instances, when used for the production of alkali-metal chlorates, solutions containing both alkali-metal chlorate and alkali-metal chloride are recirculated to the cell for further electrolysis. In yet another modification, the present cell can be utilized for the electrolysis of hydrogen chloride by electrolyzing hydrogen chloride in combination with an alkalimetal chloride. Thus, the present cell is highly useful in these and many other aqueous electrolytic processes.

The diaphragm which can be used to cover the screen cathode is a fluid permeable and halogen resistant material. Preferably, the material is asbestos deposited in situ on the outer surfaces of the cathode screen fingers facing the anode blades. However, other types of diaphragms can be used, depending on the reaction and reaction conditions contemplated. Other diaphragm materials such as those comprised of synthetic organic materials. Such as woven after-chlorinated polyvinyl chloride, polyvinylidene chloride, polypropylene, Teflon, and the like can be used. These and other suitable materials are known to those skilled in the art. The cell structure is adopted to permit use of all types of diaphragms, including sheet asbestos, deposited asbestos and synthetics which can be in the form of woven fabrics.

The above-described cell offers significant advantages over prior cells. A most important consideration is the extremely high efficiency of operation at unusually high current capacities of the order of 60,000 amperes and higher. Such high amperages provide for considerably greater productivity for a given cell room area. The novel structure cathode system of the present cell provides improved electrical conductivity to the immediate area of the cathode fingers, thereby providing a minimum voltage drop through the cell, with a substantial reduction in copper expenditures, compared to previous chlor-alkali electrolytic cells. In addition to being capable of operation at the extremely high amperages, the present cell can also be efficiently operated at lower amperages, such as at about 30,000 amperes or less and higher amperages upwards to 100,000 amperes.

While there have been described various embodiments of the present invention, the apparatus described is not intended to be understood as limiting the scope of the invention. It is realized that changes therein are possible. It is further intended that each element recited in any of. the following claims is to be understood as referring to all equivalent elements for accomplishing the same results in substantially the same or equivalent manner. It is intended to cover the invention broadly in whatever form the principles thereof may be utilized.

What is claimed is:

1. A cathode assembly for an electrolytic cell comprising a lead-in bus bar, a bus bar strip and an enclosure having sidewalls, to at least one of which are attached a plurality of internally reinforced foraminous screen fingers, said fingers extending substantially across the interior of said walled enclosure, said internally reinforcing means being attached to at least one side of said enclosure and in electrical contact with said screen fingers, said attachment being adjacent to said bus bar strip on the exterior of a side of said enclosure, said bus bar strip being substantially the height of the reinforcing means at the point of the reinforcing attachment and said bus bar strip being joined to a lead-in bus bar.

2. The apparatus of claim 1 wherein the internal reinforcing means of said cathode finger is a corrugated ferrous plate.

3. The apparatus of claim 1 wherein the bus bar strip attached to the exterior of one side of said sidewall enclosure is a continuous copper strip of substantially the height of the reinforcing means at the point of attachment to the sidewall enclosure.

4. The apparatus of claim 1 wherein the bus bar strip is a plurality of copper strips wherein the number of said strips ranges up to the number of internally reinforcing means.

5. The apparatus of claim 1 assembled between a cell bottom and a cell top.

6. The apparatus of claim 1 wherein a plurality of bus bar strips are included, which are vertically positioned copper strips in spaced relationship with each other.

7. The apparatus of claim 6 wherein the space between the vertically positioned copper strips is substantially filled with welding.

8. The apparatus of claim 7 wherein the weld seams are adjacent to the internally reinforcing means.

References Cited UNITED STATES PATENTS 1,855,497 4/1932 Stuart 204283 2,409,912 10/1946 Stuart 204266 2,447,547 8/1948 Stuart 204266 2,916,430 12/1959 Van Winckel et al. 204283 XR 2,987,463 6/1961 Baker et al. 204-266 3,242,059 3/1966 Cottam et al. 204-98 JOHN H. MACK, Primary Examiner D. R. JORDAN, Assistant Examiner U.S. Cl. X.R. 204--266 

